1. Field of the Invention
This invention relates to a stress measurement method and its apparatus. The stress of material in the process, goods (for example, single crystal of semiconductor etc.) and unknown stresses in the composed parts under the power station, high pressure plants, airplane, vehicles, various kinds of device, and the material of parts inthe other constructions etc. are especially able to rapidly quantitatively obtain by use of this invention.
2. Related Art
The various kind of vehicles or constructions mainly made of metals are generally used for semi permanent term. Contrarily, each part is necessary to be repaired or exchanged with a lapse of determined time because of its partial damage.
In the various kinds of vehicle, not only axle supporting weight of vehicle but also connective bolt and power transmission are under continuously or repeatedly dynamical or static load. The material having the strength enough to endure the stresses owing to the above various loads is selected and used as the material of these parts. Even such case, it is necessary to do about periodical inspection of whole equipment and exchange of the damageable place.
The understanding of the magnitude and fluctuation of inner stress occurred by applied load gives important information to estimate the fatigue of the concerned material and to study on the improvement of material or the shape. Therefore the strict measurement of stress in these parts have been performed especially by use of ultrasonic waves in most cases, as shown in the patent 5-203513.
In the invention described in the official report Patent No. 5-203513 (the measurement method of the axle stress of bolt by the ultrasonics), measurements of stress both longitudinal and transverse waves are necessary for the concerned material to be measured. Therefore these measurements are always complicated in the preparation of both sensors of longitudinal and transverse waves. Moreover in this patent reference 1, the relation between the sound velocity ratio R and the stress σ was not disclosed, so it was difficult to apply for industrial use.